Punch press having a die cushion



arch 18, 1947. BQ WERNER $41279 I PUNCH PRESS HAVING A DIE cusruou FiledNov. 59'. 1942 @aicnted Mar. 18,1947

Nines PUNCH PRESS HAVING A CUSEON Herbert B. Werner, Chicago, Ill...assignor to Verson Allst'eel Press Compam, Ghicago, m, a corporation ofDelaware Application November 30, 1M2, Serial No. 467,42fi

(ca. ire-.45)

5 Claims. l

The present invention relates to punch presses. More particularly, itrelates to punch presses having die cushions.

I For performing some types of metal drawing operations on a punch pressit is necessary to hold the rnetalblank tightly in place during thedrawing step, so that the metal will flowsmoothly into the die cavitywithout the formation of wrinkles. been used for accomplishing thisblank holding step.

One arrangement is to use a multiple action press, that is, a presshaving two or more slides operating difierentially with respect to eachother. For-performing the above operation a blank holding slide firstmoves downwardly and clamps the blank in place. When it has reached theblank holding position, it stops and remains in. this position until thecompletion of the drawing operation, after which it recedes prior to, oralong with the slide carrying the metal drawing memher. The principaldimculty with multiple action presses having blank holding slides isthat they are expensive. Another expedient has, therefore, beenfrequently used in conjunction with single action presses foraccomplishing the same general objective. This arrangement is known as adie cushion.

With the die cushion arrangement, the reciprecalling die is surroundedby an annular blank holding member, or clamping ring, which movestherewith. This blank holding member during the downward stroke of thepress is brought against the blank and squeezes the blank against andraw ring surrounding the lower fixed die member. Thisannular draw ringis yieldingly supported upon a die cushion and moves downwardly underrestraint along with the reciprocating member.

Cushions of this type are usually hydraulic, that is, a hydrauliccylindersupports the draw ring, and the fluid, in the cylinder ispermitted to In the past, two arrangements have tion to provide a presshaving a die cushion of large capacity, which is adapted to'beoperatedwith considerably less power than has heretofore been thought possible.

Yet another object of the present invention is to provide a novel punchpress die cushion arrangement such that the energy required to operatethe die cushion comes only partially from the press flywheel and crank.

Yet another object of the present invention is to provide a novelarrangement for duplicating escape against the restraining effect of apressure control valve.

The die cushion operates and dissipates energy during substantially theentire length of the stroke. It necessitates the loss of considerableenergy, therefore. to operate a die cushion in conjunction with a punchpress. Because of the energy required to ouerate a die cushion, suchcushions have never heretofore been feasible on presses of medium orlarge size; For instance, a. punch press die cushion which supports adraw ring against a pressure of say three hundred tons,

and which moves through astroke ofisix inches the performance cl .9.double action press with a single action press.

Still another object of the present invention is to provide a novel diecushion which can exert the same, or greater, draw ring pressures aspreviously used, but which requires only approximately lb% of the energyheretofore thought necessary for its operation.

Yet another object of the present invention is to provide a novel punchpress accessory which serves the usual blank holding function of anordinary tyne die cushion without requiring more than MW, of the energyconventionally used in a die cushion of similar capacity.

Yet another object or the present invention is to provide a novel diecushion arrangement which accomplishes the above set forth objective andwhich further has an upward stripping capacity or approximately the sameintensity as the down ward capacity or" the cushion.

Yet another object of the present invention is to accomplish all of theabove in a simple manner and at comparatively low cost.

Other objects and advantages will become apparent from the followingdescription of a pre= ferred embodiment of my invention, illustrated inthe accompanying drawing, in which similar characters of reference referto similar parts, and

in which the figure is a diagrainmatic sectional view or a punch pressand die cushion, arrangement incorporatingthe present invention.

Inasmuch as the construction of iswell known, and since the presentinvention'is of a comparatively simple nature from a niechanicalstandpoint, and, therefore, will be read= ily understood by all skilledin the art, the invention has been illustrated diagrammatically. In

punch presses the figure I have illustrated a typical punch press slide,indicated by the numeral l0, having a die l2, provided with a cavity i4,and an annular blank holding surface or clamping ring it.

Beneath the slide I have shown a typical bolster plate ll supporting apunch member 20, which is generally complementary-in shape to the cavityl4. This punch is surrounded by an annular draw ring 22, in alignmentwith theblank holding surface l5.

The bolster plate is supported upon a bed It, while a second plate 24rigidly secured in the press frame therebeneath supports the piston 26of a die cushion indicated generally by the numeral 28. This piston isfitted to a cylinder 30, which is movable upwardly and downwardlyrelative to piston 28, and which supports the draw ring 22 upon pins".-Vertical movement of the draw ring 22 is therefore possible whenaccompanied by similar movement of the cylinder 30.

The space within the piston 28 and the cylinder 30 is filled withhydraulic fluid 33, and this fluid communicates through a pipe 36connecting the draulic fluid, which is maintained under air pressure,the air being communicated to the reservoirby a pipe 38. There is anoutlet 40 at the lower portion of the reservoir, which is connectedthrough a check valve 42 with the pipe 36. Thus, any time pressure isreleased from the surface of the draw ring 22, that is; whenevertheslide in moves upwardly, air pressure within the tank 34 will forcehydraulic fluid through the outlet 43, through the check valve 42,through the pipe 36, and into the cylinder 28 to elevate the cylinderand draw ring.

During the downstroke of the press, that is, while the draw ring 22 ismoving downwardly, hydraulic fluid will be forced from the cylinder 28,but will be prevented from entering the outlet 40 of the tank 34 byreason of the closing of the check valve 42. This fluid, however, canpass through a branch conduit 44 leading to the tank 34. This branchconduit is equipped with a pressure control valve 46, which prevents theflow of fluid therethrough until a certain predetermined pressure hasbeen imposed upon the inlet side of this valve. In other words, nofluid, excepting a small amount which may leak through the check valve42, can return to the tank 34 during the downstroke of the press untilthe pressure upon the fluid in the die cushion cylinder 28 has reachedthe predetermined pressure at which the control valve 46 is set.

Beneath each end of the slide I0, I have located what may be referred toas energy recovery cylinders 48; These two cylinders may be consideredas identical, two being used to balance the press as will hereafterappear. Inasmuch as they are substantially identical, only one of theserecovery lower end of this piston passes through an opening 54 locatedat the lower end of the cylinder, and a packing gland 58 may be used toseal the openingaround this piston. The upper end of the piston isconnected to a piston rod 58, which passes upwardly through a closefitting opening,

.the pipe 38 by a branch pipe 80.

The area of the effective portion of the piston 52, that is, the annularsurface at the upper end of the piston, is approximately 45% of theeifective area of the piston 28, thus, the effective area of the twopistons 52 together is approximately 90% of the area of the piston 26.

For a purpose to be described presently, a solenoid relief valve 82 isconnected in parallel with the check valve 42. This solenoid valve is ofthe type which remains closed excepting when energized. It receives itsenergy from a, source of electrical potential indicated by the battery64, connected to the solenoid valve through a normally open limit switch88. The limit switch is located adjacent to the cushion cylinder 30where a bracket 88 attached to the side of the cushion will close thelimit switch and open valve 62 when the cushion is in its uppermostposition. Immediately after the cushion starts its downward movement,the switch 66 will be opened, thereby closing Valve 62.

This device operates in the following manner: During the downward strokeof the slide to, the blank holding surface or clamping ring 16 isbrought against the upper face of the draw ring 22. Prior to contactbetween the faces l6 and 22, the cylinders 48 are kept filled with fluidforced from the reservoir 34. As soon as contact is made, the draw ringis forced downwardly, thus tripping the limit switch 66 and pushing thehydraulic fluid from the cushion. 28. The hydraulic fluid flows into thepipe 38, where it is connected by the pipe to the recovery cylinders 48.Within the recovery cylinders the fluid pressure is brought to bearagainst the upper annular faces of the pistons 52 and urges thesepistons downwardly. Inasmuch as 90% of the fluid forced from the diecushion enters the recovery cylinders 48, it will be appreciated thatthe two piscylinders need be described, however.

Referring to the left hand recovery cylinder 48, it will be seen thatthis cylinder is secured in an opening in the bed l8 and is provided ina ton rods 58 will pull downwardly upon the slide ill with of the energydeveloped in the die cushion 28, less small frictional losses.

From the above it will be seen that 90% of the energy required tocollapse the die cushion 28 will be developed within the recoverycylinders and, therefore, will actually have come from the die cushionitself. Therefore, the energy required to be stored in the flywheel forurging the die cushion downwardly is only 10% of the energy actuallyabsorbed by the die cushion in holding the blank.

It will be appreciated that the effective areas of the pistons 52 couldtheoretically be exactly equal to the efiective area of the die cushion,in which case of the energy, less frictional losses, would be returnedto the slide, In the construction of punch presses, however, wherefrequently no two presses are alike and each one must be engineeredseparately, and also inasmuch as there may be some slight leakage in thecheck valve 42, it will be seen that it is generally not feasible toattempt to recover all of the energy developed by the die cushion. Thegiven figure of 90% is suihciently high, however, to enable recovery ofsubstantially all of the energy, and still low enough to overcomedifficulties incident to engineering and constructing the press.

Since only 90% of the hydraulic fluid forced from the cushion 28 canenter the recovery cylinders 48, the extra %.,minus whatever-smallamount leaks through the check valve 42 will be returned to thereservoir 34 through the pressure control valve 46. After the completionof the downward stroke, the slide Ill moves upwardly,i-thus lifting thepistons 52, therebyreturning the hydraulic fluid from the recoverycylinders 48 to the cushion 28. The amount of hydraulic fluid thusreturned will not completely fill the cushion, inasmuch as the capacityof the die cushion is greater than the capacity of the recoverycylinders 48. The

additional hydraulic fluid, in the present instance approximately 10% isforced into the die cushion from the reservoir 34 by reason of the airpressure therein, thus returning the die cushion to the upper limit ofthis stroke. 7

, After the die cushion has reached the upper limit of its stroke, nomore hydraulic fluidv can be accommodated in the die cushion cylinder.The slide 10 and pistons 52 continue their upward movement however,thereby forcing hydraulic fluid into the pipe 60. If it were not for thesolenoid relief valve 62, this excess fluid would necessarily have tofind its way back through the high pressure relief valve 46, therebydissipating considerable energy. As has been explainedpreviously-however, the die cushion opens the limit switch 65 as soon asit reaches the upper limit of its stroke, thereby opening the reliefvalve 62 and permitting fluid forced into the pipes 60 by the pistons 52after the die cushion has completed its upward stroke to return to thereservoir 34 through the valve 62 rather than through the valve 46. V

During the upward stroke of the press considerable stripping action canbe developed by the die cushion if necessary. Under normal conditionsthe die cushion will accommodate more hydraulic fluid during its upwardstroke than is forced into the pipes 60 by the pistons 52, this excessfluid being. supplied through the check valve 42 from the reservoir 34under approximately 100 pounds per square inch pressure. However, shouldthe die cushion stick at any point and not continue upward movementalong with the slide Ill, the continued upward movement of the pistons52 will close the check valve 42 and raise the pressure in the diecushion until the high pressure relief valve 46 opens.

tributed. As a matter of fact, only one cylinder need beused if thiscylinder directs its efiort against the slide at its substantial center.For instance, a single cylinder of this type could be located above theslide inthe press crown. or in This develops in the die cushion the sameforce as is used for blank holding purposes. This high stripsome similarcentral location. The construction illustrated is preferred, however,inasmuch as die cushions are frequently installed upon a previouslyconstructed press, and by having the recovery cylinders and die cushionclosely associated beneath the bolster plate, the design of theseelements and the hydraulic circuit is simplified,

although as explained above, if desired, the recovery cylinders may bearranged in other locations if it appears desirable in some particularinstance.

While I have shown and described particular embodiments of my invention,it will be apparent I to those skilled in the art that numerousmodifications and variations may be made without departing from theunderlying principles of the invention. I therefore desire, by thefollowing claims, to include within the scope of the invention all suchmodifications and variations by which substantially the results thereofmay be obtained by substantially the same or equivalent means.

I claim:

1. A die cushion arrangement for use with a punch press having a frame,a slide reciprocable therein, and means for reciprocating said slide,comprising: a die cushion having a variable volume fluid chamber andlocated within said frame,

for supporting a draw ring or similar element, recovery piston andcylinder means connected between the press slide and the frame forurging the slide downwardly when hydraulic fluid is forced into saidpiston and cylinder means, means including a closed fluid circuitextending between said chamber and said piston and cylinder meanshydraulically connecting said recovery piston and cylinder means to saiddie cushion so that fluid forced from said die cushion is communicatedto said recovery piston and cylinder means, means including a source offluid under pressure and a check valve enabling the fluid to flow fromsaid source to said closed fluid circuitfor fillin said piston andcylinder means with fluid during that portion of, the down stroke of apress cycle before said die cushion is acted upon by the press slide,said check valve remaining closed during the up stroke of the presscycle to confine the fluid to said closed circuitso that the fluidforced from said piston and cylinder means is communicated to said diecushion to restore it to its "rest position, and hydraulic pressurerelief means to permit the escapeunder restraint of hydraulic fluid fromsaid closed fluid circuit when a predetermined pressure is reached insaid circuit on both the down and up strokes of the press cycle.

2. A punch press comprising a frame, a slide reciprocable in said frame,a die cushion associated with said frame, a member on said slide forcollapsing said die cushion when said slide moves toward said diecushion, a cylinder immovably mounted relative to said frame, conduitmeans hydraulically connecting said cylinder with said die cushion, apiston reciprocable in said cylinder and rigidly secured to said slide,whereby the major portion of the energy transferred from said collapsingmember to said die cushion is recushion with said hydraulic storagemeans, said connecting means including a pressure relief valve, otherconduit means connecting said storage means with said die cushion meansand said cylinder, the last said conduit means including a check valvefor preventing flow of hydraulic'fluid from said die cushion meanstoward said storage means thereby to communicate the fluid forced fromsaid cylinder to said die cushion on the up stroke of a press cycle torestore said die cushion to "rest position, and means to maintain thefluid in said storage means under pressure, whereby said cylinder isfilled with fluid through said check valve during the initial portion ofthe down stroke of a press cycle.

3. In a press having a frame, a slide movable in opposite directions, afluid operable cushion means cooperating with said slide to cushion thepressing action thereof, a cylinder-piston assembly operativelyconnected between the 'slide and the frame, a source of fluid underpressure, and conduit means interconnecting the cushion means, thecylindenpiston assembly and the source of fluid, a check valvein saidconduit means permitting flow of fluid to the cylinder-piston assemblyduring the initial portion of a press cycle before the slide acts uponthe cushion means, whereby pressure fluid expelled by the cushion meanswhen moved in one direction is supplied to the cylinder-piston assemblyto effect operation thereof to move the slide in the pressing direction,and said check valve in the conduit means preventing flow of fluid tosaid source, whereby pressure fluid expelled from the cylinder-pistonassembly upon the initial portion of the return movement of the slide isconveyed to. the cushion means to move it in the opposite direction.

4. In a press having a slide movable in opposite directions and fluidoperable cushion means cooperating with said slide to cushion thepressing action thereof, a cylinder-piston assembly operativelyconnected to said slide, and means including closed circuit conduitmeans interconnecting the cushion means and cylinder-piston assembly, asource of fluid under pressure, and a conduit including a check valveand a high pressure relief valve connecting said source to said circuit,whereby pressure fluid expelled by said cushion means when movedin onedirection is supplied by the cylinder-piston assembly to efiectoperation thereof to move the slide in the pressing direction, and thecheck valve preventing flow of fluid to the source whereby pressurefluid expelled from said cylinder-piston assembly upon th returnmovement or the slide is conveyed to the cushion means to move it in theopposite direction. l

5. In a press having a slide movable in opposite directions and fluidoperable cushion, means cooperating with said slide to cushion thepressing action thereof, a cylinder-piston assembly operativelyconnected to said slide, and means including closed circuit conduitmeans interconnecting the cu hionmeans and the cylinder-piston assembly,a source of fluid under pressure, a concheck valve, and means foropening said valve means when the cushion means is in its normalposition.

' r HERBERTB. WERNER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,664,485 Rode Apr. 3, 19281,861,337 Ernst May 31, 1932 2,269,778 Merrill Jan, 13, 1942 2,294,451Ernst Sept. 1, 1942 2,300,162 Maude Oct. 27, 1942 2,305,610 Ernst Dec.22, 1942 2,354,003

Ernst Jilly 18, 1944

